The hydraulic fracturing of subterranean formations is now a well known concept for improving the productivity of subterranean hydrocarbon formations. In the usual process various liquids, such as crude oil, diesel fuel, kerosene, water, etc., with or without propping agents, such as sand suspended therein, have been applied under pressure to subterranean formations. By increasing the pressure upon the hydraulic liquid the formation is placed under stress so as to break-down or part or `fracture.` Such fracturing, however, has its limitations in that very often the liquid utilized is highly viscous requiring large and multiple pumping equipment to achieve high injection rates and pressures to reach the `formation break-down pressure` and to extend the fracture. Generally, when formation break-down pressure is reached and fracturing occurs, a large pressure drop results. The pumps then must be capable of rapidly supplying large volumes of additional fracturing liquid in order to maintain and extend the fractures formed. In addition, the use of such liquids often requires additional treatment or chemicals to increase viscosity and/or gel strength and/or to improve fluid loss properties of the hydraulic liquids to the formation and/or improve the sand and propping agent carrying capabilities and/or other reasons. However, under present times it has become important to conserve such liquids as crude oil heretofore utilized in the fracturing processes and find other medium to achieve the fracturing or more importantly the extension of existing fractures in subterranean formation. Further, the disposal of large quantities of fracturing fluids or the additives therein will damage the environment i.e., air, land or water and is undesirable.
Low permeability gas wells are particularly sensitive to the injection of hydraulic fracturing liquids and the additives therein which have tendency to plug the gas pores of a formation and instead of increasing will greatly hinder or cease the production therefrom. In many instances it is necessary to complete the well by swabbing or other operation in order to return the fracture fluid and to initiate production.
Others have taught the use of aerated well treatment compositions, but have not described a stable foam having the quality standards nor have they described the process to achieve the quality fracturing or fracture extension fluids as set forth in this invention. See for example:
U.S. Pat. No. 3,100,528 -- Plummer et al., teach the need of a gas cushion injector prior to injection of an aerated well treating reactant. The gas injection rates taught are insufficient to maintain and create a foam of quality defined herein.
U.S. Pat. No. 3,136,361 -- Marx, which teaches prefracture with compressed gas followed by injection of aerated liquid to extend the fracture. The liquid is treated to achieve the necessary characteristics desired for fracture extension.
U.S. Pat. No. 3,245,470 -- Henry, which is a multi-hydraulic fracturing process wherein an aerated liquid is injected to plug preformed fractures followed by additional hydraulic fracturing.
U.S. Pat. No. 3,323,593 -- Foshee et al., teach a liquid fracturing base formed of two normally immiscible liquids (principal and conditioning), a surfactant, and a gas in an amount in excess of that which will dissolve in the liquid at the formation temperature and pressure.